factcheck

name	factcheck
description	Verify statistics and claims in blog posts by fetching cited source URLs and checking if the claimed data actually appears on the page. Extracts all statistical claims (numbers, percentages, named sources), fetches each cited URL via WebFetch, and scores match confidence (exact match 1.0, paraphrase 0.7-0.9, not found 0.0). Flags uncited claims as UNVERIFIED. Use when user says "fact check", "verify statistics", "check sources", "validate claims", "factcheck", "source verification", "核查", "驗證數據".
user-invokable	true
argument-hint	[file]
license	MIT

Blog Fact-Check

Verify statistics, claims, and source attributions in blog posts.

Workflow

Step 1: Read the Blog Post

Read the target file and identify all sections containing data claims.

Step 2: Extract Statistical Claims

Scan the full text for every claim that includes a number, percentage, dollar amount, or named source. Build a claims list with these fields:

Field	Description
claim_text	The exact sentence or phrase containing the statistic
value	The numeric value (e.g., "42%", "$1.2M", "3x")
attribution	Named source if present (e.g., "HubSpot", "Gartner 2025")
url	Cited URL if present
location	Heading or line number where the claim appears

Step 3: Verify Cited Claims

For each claim that includes a URL:

1. Fetch the source page via WebFetch
2. Search the returned content for the specific numeric value
3. If exact value found, check surrounding context matches the claim topic
4. Assign a confidence score

Process claims sequentially to avoid rate-limiting source sites.

Step 4: Flag Uncited Claims

For claims without a URL:

• Mark status as UNVERIFIED
• Suggest a search query the user can run to find a source

Step 5: Generate Verification Report

Verification Scoring

Score	Status	Criteria
1.0	VERIFIED	Exact number found on cited page in matching context
0.7-0.9	PARAPHRASE	Similar data found but with different wording, rounding, or timeframe
0.3-0.6	WEAK	Source page exists and covers the topic but the specific statistic is not visible
0.0	NOT FOUND	Cited page does not contain the claimed data anywhere
N/A	UNVERIFIED	No source URL provided for the claim

Output Format

Verification Report: [Post Title]

File: [path] Claims found: [total] Verified: [count] | Paraphrase: [count] | Weak: [count] | Not Found: [count] | Unverified: [count]

#	Claim	Source URL	Score	Status	Notes
1	"73% of marketers..."	https://example.com/report	1.0	VERIFIED	Exact match found
2	"5x ROI improvement"	https://example.com/study	0.8	PARAPHRASE	Source says "nearly 5x"
3	"60% prefer video"	(none)	N/A	UNVERIFIED	Try: "video preference statistics 2025"

Recommended Actions

• [List claims that need source URLs]
• [List claims with weak or not-found scores that need replacement sources]

Limitations

• Paywalled content: WebFetch cannot access content behind login walls. Score as WEAK (0.5) with a note.
• Dynamic pages: JavaScript-rendered content may not be available via WebFetch.
• PDF sources: WebFetch may not extract PDF text reliably. Flag for manual verification.
• Archived pages: If a URL returns 404, suggest checking web.archive.org.
• Rate limits: Process no more than 10 URLs per run. If a post has more than 10 cited URLs, verify the first 10 and list the remainder as SKIPPED.